perf build: Conditionally add feature check flags for libtrace{event,fs}

This avoids reported warnings when the packages are not installed.

[namhyung]: Removed the dummy assignment and unnecessary ifeq checks.

Fixes: 0f0e1f445690 ("perf build: Use pkg-config for feature check for libtrace{event,fs}")
Signed-off-by: Guilherme Amadio <[email protected]>
Cc: Leo Yan <[email protected]>
Cc: Thorsten Leemhuis <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Namhyung Kim <[email protected]>

0 files changed, 0 insertions, 0 deletions